1. Field of the Invention
The present invention relates to a control arrangement for controlling web unwinding equipment for unwinding a roll containing a web to be used in a web-fed rotary printing machine.
2. Description of the Related Art
A control arrangement for controlling web unwinding equipment is disclosed in German reference DE 41 28 860 A1 including an integrator which sets the gain of a control loop and controls the central position of a dancer roll. A problem with this device is that a high gain is required to control the central position of the dancer roll. Furthermore, this device provides control only by introducing a negative torque via a brake.
Another control arrangement for controlling web unwinding equipment is disclosed in German reference DE 195 20 955 A1 in which a four-quadrant drive is used. This type of drive is very complicated and expensive. A further problem is that the control arrangement is pure rotational speed control, which always has to calculate its rotational speed signal from the roll diameter or a parameter related to the roll diameter.
It is an object of the present invention to provide a control arrangement for controlling web unwinding equipment used for unwinding webs from a wound roll for feeding the web to a web-fed rotary printing machine without a diameter signal from the wound roll using the interplay between drive and brake to control the unwinding.
According to the invention, the object is achieved by a control arrangement for controlling web unwinding equipment used for unwinding a web from a wound roll for feeding a web-fed rotary printing machine, the web unwinding equipment including a swing roller arranged in a loop of the web for keeping a constant tension on the web, wherein the swing roller is movable to maintain the constant tension, the control arrangement comprising, a transmitter having a transmitter output and operatively connectable for monitoring a position of the swing roller, the output being dependent on the position of the swing roller, an integrator having an input connected to the transmitter output and having an integrator output, a proportional and differential element having an input connected to the transmitter output and having a proportional and differential output, an adder having inputs connected to the integrator output and the proportional and differential output and having an adder output, and a braking element operatively connectable to the wound roll for generating a braking force for braking the wound roll, wherein a value of the braking force is responsive to the adder output.
A control arrangement for controlling web unwinding equipment used for unwinding a web from a wound roll for feeding a web-fed rotary printing machine, comprising, a swing roller operatively arranged in a loop of the web for keeping a constant tension on the web, wherein the swing roller is movable from a central position to maintain the constant tension, a transmitter having a transmitter output and operatively connectable for monitoring a position of the swing roller, the output being dependent on the position of the swing roller, a two-quadrant drive operatively connectable to the wound roll for applying a torque to a core of the wound roll, thereby exerting an influence on the rotational speed of the wound roll, a motor controller for controlling the two-quadrant drive, the motor controller being connected to a synchronous rotation speed input signal comprising a rotational speed of the web divided by the diameter of a replacement wound roll, an integrator having an input connected to the transmitter output and having an integrator output, a first polarity-dependent element having an input arranged for receiving the transmitter output and having a first polarity-dependent output, a proportional and differential element having an input connected to the first polarity-dependent output and having a proportional and differentiated output, a second polarity-dependent element having an input arranged for receiving the transmitter output and having a second polarity-dependent output connected to the motor controller, an adder having inputs connected to the integrator output and the proportional and differentiate output and having an adder output, a braking element operatively connectable to the wound roll for generating a braking force for braking the rotation of the wound roll, and an electro-pneumatic converter having an input connected to the adder output and an electro-pneumatic converter output connected to the braking element, wherein a value of said braking force is responsive to said electro-pneumatic converter output.
The control arrangement according to the present invention permits the operation of a four-quadrant control system without requiring the calculation of a diameter signal. When the machine is being started up with a wound reel of unknown diameter, a deviation of the swing-roll system from the central position occurs which is only brief, low and therefore unimportant for the web tension. After the initial deviation, no residual error occurs and the swing-roll system is controlled to the central position.
The four-quadrant control system is formed from a two-quadrant drive and a brake, wherein the positive torques, i.e., the drive and acceleration of the wound reel, are controlled by the two-quadrant drive and the negative torques, i.e., the braking of the wound reel, is performed and controlled by the brake.
A significant advantage of the present invention applies in particular to the torque control system of the control arrangement in that the present invention permits the implementation of a braked roll changer with an auxiliary drive.
A further advantage of the present invention is that the web unwinding equipment may also be controlled solely via the brake in the event of a failure or malfunction of the two-quadrant drive. In this emergency-mode of the control arrangement, the web tension is controlled only with the aid of the brake.
It is also an advantage of the present invention that a positive torque is applied to the wound roll by the drive. In the event of positive acceleration values of the web or severe fluctuations in speed which may occur, for example, when threading paper, the wound roll must be accelerated in response to the tension on the web.
In addition, the present invention achieves a high control stability in that pilot brake control is implemented via the integrator in a manner independent of the coefficient of friction and acts as a damping system. As a result, the control loop gain may be kept relatively low.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.